Iron(III) complexes of ethylenediamine derivatives of aminophenol ligands as models for enzyme-substrate adducts of catechol dioxygenases

Article abstract of DOI:10.1016/j.ica.2012.10.015

In the present work, six N,N'-dimethylethylenediamine derivatives of substituted aminophenol ligands (H₂L^NEX, X: C, B, M, BM, Bu and OB) were synthesized by a convenient, green procedure. The mentioned ligands were characterized by 1

Full text of DOI:10.1016/j.ica.2012.10.015

Inorganica Chimica Acta 395 (2013) 124–134
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Iron(III) complexes of ethylenediamine derivatives of aminophenol ligands
as models for enzyme–substrate adducts of catechol dioxygenases
b
b
ˇ ´ c
Touraj Karimpour a, Elham Safaei a, , Andrzej Wojtczak , Zvonko Jaglicic , Anna Kozakiewicz
⇑
a Institute for Advanced Studies in Basic Sciences (IASBS), 45195 Zanjan, Iran
b Nicolaus Copernicus University, Department of Chemistry, 87-100 Torun, Poland
c Institute of Mathematics, Physics and Mechanics & Faculty of Civil and Geodetic Engineering, University of Ljubljana, Jadranska 19. SI-1000 Ljubljana, Slovenia
a r t i c l e i n f o
a b s t r a c t
In the present work, six N,N0-dimethylethylenediamine derivatives of substituted aminophenol ligands
(H2LNEX, X: C, B, M, BM, Bu and OB) were synthesized by a convenient, green procedure. The mentioned
ligands were characterized by 1H NMR and IR spectroscopies. iron complexes (FeLNEX, X: C, B, M, BM, Bu
and OB) of mentioned ligands, have been synthesized and characterized by IR, UV–Vis, elemental analy-
sis, single crystal X-ray diffraction, magnetic susceptibility studies and cyclic voltammetry techniques. X-
ray structure analysis has revealed that Fe(III) centers were surrounded by two phenolates, two amine
nitrogens and two oxygen atoms of acetylacetonate ligand similar to the proposed catechol-bound
intermediate for catechol dioxygenase. The variable temperature magnetic susceptibility indicates
paramagnetic iron(III) in monomer complexes. All complexes undergo a metal-centered reduction, and
a ligand-centered oxidation.
Article history:
Received 11 June 2012
Received in revised form 19 September 2012
Accepted 9 October 2012
Available online 2 November 2012
Keywords:
Catechol dioxygenase
Non-heme
Model complexes
Intradiol-cleaving
Extradiol-cleaving
Mononuclear iron(III) complexes
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
ethylenediamine units (Scheme 2). (2) Synthesis of the acetyl-
acetonato iron(III) complexes of mentioned ligands as models for
Catechol dioxygenases are mononuclear non-heme iron en-
zymes which catalyze the oxidative cleavage of toxic environmen-
tal catechol substrates [1–3]. Soil bacteria containing these
enzymes provide their carbon and energy through aerobic biodeg-
radation of aromatic hydrocarbons [4–6] with concomitant inser-
tion of molecular oxygen into the aromatic ring of the substrate
resulting in production of aliphatic acids.
mononuclear non-heme iron intermediates. (3) Significance of Le-
wis acidity of iron(III) centers for the structural and electronic
properties of dioxygenase–substrate adduct models.
2. Experimental
2.1. Materials and physical measurements
Catechol dioxygenases subdivided into two classes on the basis
of the site of aromatic ring cleavage [7]: The intradiol catechol
dioxygenases, utilize mononuclear iron(III) centers to catalyze
the oxidative cleavage of the carbon–carbon bond between the
two phenolic hydroxyl groups, while the extradiol-type enzymes
contain a non-heme iron(III) co-factor, cleave the adjacent car-
bon–carbon bond. (Scheme1).
Many of the reported mimics of the catechol dioxygenases have
focused on the tetradentate all-nitrogen donor ligands, [8–12] and
complexes with phenolato groups as structural and functional
models for the catecholate-iron(III) form of catechol dioxygenases
[13–20].
Reagents or analytical grade materials were obtained from com-
mercial suppliers and used without further purification, except
those for electrochemical measurements. Elemental analyses (C.
H. N.) were performed by the Isfahan University of Technology.
Fourier transform infrared spectroscopy on KBr pellets was per-
formed on a FT IR Bruker Vector 22 instrument. NMR measure-
ments were performed on a Bruker 400 instrument. UV–Vis
absorbance digitized spectra were collected using a Ultrospec
3100 Pro spectrophotometer.
Magnetic susceptibility were measured from powder samples
of solid material in the temperature range 2–300 K by using a
SQUID susceptometer (Quantum Design MPMS-XL-5) in a mag-
netic field of 1000 Oe.
Herein, we describe: (1) Synthesis of new tetradentate amino-
phenol ligands containing substituted phenol and N,N0-dimethyl-
Voltammetric measurements were made with a computer con-
trolled electrochemical system (ECO Chemie, Ultrecht, The
Netherlands) equipped with a PGSTA 30 model and driven by GPES
⇑
Corresponding author. Tel.: +98 241 4153200; fax: +98 241 4153232.
E-mail address: safaei@iasbs.ac.ir (E. Safaei).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.10.015

T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
125
quantity of beige solid was formed. The solvent was decanted,
and the remaining solid residue was washed with cold methanol
to give a pure, white powder.
2.2.1.1. Synthesis of H2LNEC [6,60-((ethane-1,2-diylbis(methylaza-
nediyl))bis(methylene))bis(2,4-dichlorophenol)]. (4.00 g, 76% yield).
1H NMR (400 MHz, CDCl3, 298 K): d 2.345 (s, 6H); 2.734 (s, 4H);
3.721 (s, 4H); 6.895 (d, 2H); 7.294 (d, 2H); 10.884 (br, 2H).
IR(cmꢀ1): 3421 (OH); 2817 (C–H); 1459 (C@C, phenyl ring). m.p.
167–168 °C.
Scheme 1. Scheme of cleavage by intradiol and extradiol dioxygenases [7].
2.2.1.2. Synthesis of H2LNEB [6,60-((ethane-1,2 diylbis(methylaza-
nediyl))bis(methylene)) bis(2,4-dibromophenol)]. (5.20 g, 70 yield).
1H NMR(400 MHz, CDCl3, 298 K): d 2.331 (s, 6H); 2.723 (s, 4H);
3.707 (s, 4H); 7.064 (d, 2H); 7.579 (d, 2H); 10.964 (br, 2H).
IR(cmꢀ1): 3435 (OH); 2793 (C–H); 1455 (C@C, phenyl ring). m.p.
159–160 °C.
(ECO Chemie). A glassy carbon electrode with a surface area of
0.035 cm2 was used as a working electrode and a platinum wire
served as the counter electrode. The reference electrode was an
Ag wire as the quasi reference electrode. Ferrocene was added as
an internal standard after completion of a set of experiments,
and potentials are referenced vs. the ferrocenium/ferrocene couple
(Fc+/Fc).
2.2.1.3. Synthesis of H2LNEM [6,60-((ethane-1,2-diylbis(methylaza-
nediyl))bis(methylene)) bis(2,4-dimethylphenol)]. (3.20 g, 75% yield).
1H NMR(400 MHz, CDCl3, 298 K): d 2.216 (s, 6H); 2.241(s, 6H);
2.292 (s, 6H); 2.684 (s, 4H); 3.660 (s, 4H); 6.635 (d, 2H); 6.889
(d, 2H); 10.626 (br, 2H). IR(cmꢀ1): 3451(OH); 2813 (C–H); 1477
(C@C, phenyl ring). m.p. 131–132 °C.
Crystals of the FeLNEC, FeLNEB, FeLNEM, FeLNEBM, FeLNEBu and
FeLNEOB complexes suitable for the X-ray diffraction experiment
were obtained from the EtOH–CH2Cl2 solutions. The X-ray data
were collected with an Oxford Sapphire CCD diffractometer using
Mo Ka
radiation k = 0.71073 Å, at 293(2) K, by
x
ꢀ2h method. All
structures have been solved by direct methods and refined with
the full-matrix least-squares method on F2 with the use of SHELX97
[21] program package. The numerical absorption corrections were
applied (RED171 package of programs [22] Oxford Diffraction,
2000). No extinction correction was applied. For all structures,
positions of hydrogen atom were calculated from geometry, and
hydrogen atoms were constrained in the refinement.
2.2.1.4. Synthesis of H2LNEBM [6,60-((ethane-1,2-diylbis(methylaza-
nediyl))bis(methylene)) bis(2-(tert-butyl)-4-methylphenol)]. (4.30 g,
81% yield). 1H NMR(400 MHz, CDCl3, 298 K): d 1.443 (s, 18H);
2.288 (s, 12H); 2.656 (s, 4H); 3.677 (s, 4H); 6.679 (s, 2H); 7.040
(s, 2H); 10.666 (br, 2H). IR(cmꢀ1): 3414 (OH); 2959 (C–H); 1459
(C@C, phenyl ring). m.p. 128–130 °C.
2.2.1.5. Synthesis of H2LNEBu [6,60-((ethane-1,2-diylbis(methylaza-
nediyl))bis(methylene)) bis(2,4-di-tert-butylphenol)]. (4.50 g, 71%
yield). 1H NMR(400 MHz, CDCl3, 298 K): d 1.317 (d, 18H); 1.467
(d, 18H); 2.292 (s, 6H); 2.666 (s, 4H); 3.695 (s, 4H); 6.834 (d,
2H); 7.234 (d, 2H); 10.747 (br, 2H). IR(cmꢀ1): 3448 (OH); 2959
(C–H); 1472 (C@C, phenyl ring). m.p. 162–163 °C.
2.2. Preparations
2.2.1. Synthesis of ligands
Ligands were synthesized according to the modified literature
procedure [23,24].
A solution of phenol (24.00 mmol), N,N0-dimethylethylenedi-
amine (1.06 g, 12 mmol), and 37% aqueous formaldehyde
(4.31 mL, 58 mmol) was refluxed for 48 h. Upon cooling, a large
2.2.1.6. Synthesis of H2LNEOB [6,60-((ethane-1,2-diylbis(methylaza-
nediyl))bis(methylene)) bis(2-(tert-butyl)-4-methoxyphenol)]. (5.00 g,
H2LNEX
R1
R2
H2LNEC
H2LNEB
Cl
Cl
Br
Br
H2LNEM
H2LNEMB
H2LNEBM
H2LNEBu
H2LNEOB
Me
tBu
Me
tBu
OMe
Me
Me
tBu
tBu
tBu
Scheme 2. Amine bis(phenolate) ligands used in this study.

126
T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
88% yield). 1H NMR(400 MHz, CDCl3, 298 K): d 1.417 (s, 18H);
2.274 (s, 6H); 2.633 (s, 4H); 3.663 (s, 4H); 3.771 (s, 6H); 6.418 (d,
2H); 6.827 (d, 2H); 10.384 (br, 2H). IR(cmꢀ1): 3414 (OH); 2957
(C–H); 1460 (C@C, phenyl ring). m.p. 127–128 °C.
2.2.2. Synthesis of complexes
Triethylamine (0.20 g, 2.00 mmol) was added to a solution of
H2LNEX (1.00 mmol) in ethanol. Fe(acac)3 (0.35 g, 1.00 mmol) was
added to this solution and the resulting mixture was refluxed for
2 h, resulting in an intense dark red for FeLNEC and FeLNEB and pur-
ple solution for other complexes. Solvent was removed and the so-
lid material crystallized in 1:1 dichloromethane and ethanol
mixture.
2.2.2.1. Synthesis of FeLNEC. Yield: 0.46 g (78%). Anal. Calc. for C23-
H25Cl4FeN2O4 (591.11 g/mol) C, 46.77; H, 4.05; N, 4.65%. Found:
C, 46.65; H, 4.43; N, 4.73%. IR (KBr, cmꢀ1): 3447, 2895, 1580,
1524, 1456, 1363, 1317, 1271, 1217, 1173, 1056, 1019, 928, 866,
759, 662, 575, 465, UV–Vis in CH2Cl2: kmax, nm (e
, Mꢀ1 cmꢀ1):
290 (25149), 500 (7714).
Fig. 1. Electronic absorption spectra of FeLNEX (X: C, B, M, BM, Bu and OB) in
(4.7 ꢂ 10ꢀ5 M) CH2Cl2 solution.
2.2.2.2. Synthesis of FeLNEB. Yield: 0.56 g (73%). Anal. Calc. for C23-
H25Br4FeN2O4 (768.92 g/mol): C, 36.01; H, 3.27; N, 3.72%. Found:
C, 35.88; H, 3.40; N, 3.64%. IR (KBr, cmꢀ1): 3446, 2866, 1574,
1523, 1451, 1360, 1316, 1275, 1154, 1018, 927, 855, 712, 562,
of the reagents, no additional solvent is required since it is already
present in the reagent solution.
479, 427, UV–Vis in CH2Cl2: kmax
, nm (e,
Mꢀ1 cmꢀ1): 289
The iron(III) complexes were synthesized by the following pro-
cedure (Eq. (1)).
(22521), 518 (5128).
2.2.2.3. Synthesis of FeLNEM. Yield: 0.36 g (70%). Anal. Calc. for C27-
H37FeN2O4 (509.44 g/mol): C, 63.53; H, 7.02; N, 5.46%. Found: C,
63.53; H, 7.50; N, 5.49%. IR (KBr, cmꢀ1): 3448, 2968, 2907, 1586,
1518, 1469, 1370, 1313, 1266, 1158, 1059, 1021, 866, 819, 744,
R1
R2
O
O
N
N
O
O
O
O
O
Reflux/2h
663, 593, 543, 506, 470. UV–Vis in CH2Cl2: kmax, nm (e
, Mꢀ1 cmꢀ1):
Fe
Fe
R
+
HO
OH
R
N
R
O
2 NEt
EtOH
O
278 (23892), 529 (6197).
O
R
R
N
H LNEX
R
FeLNEX
2.2.2.4. Synthesis of FeLNEBM. Yield: 0.48(81%). Anal. Calc. for C33H49-
FeN2O4 (593.60 g/mol): C, 66.35; H, 8.13; N, 4.76%. Found: C, 66.66;
H, 8.48; N, 4.71%. IR (KBr, cmꢀ1):3414, 2956, 2911, 2863, 1724,
1591, 1521, 1451, 1378, 1306, 1266, 1023, 869, 808, 709, 594,
ð1Þ
The structures and purity of complexes have been confirmed by
X-ray single crystal analysis and IR spectroscopy, as well as elemen-
tal analysis. IR spectra were recorded in the region 400–4000 cmꢀ1
with samples as KBr disks. In IR spectra of complexes, the strong
and sharp OH stretching band of the phenols around 3300–
3500 cmꢀ1 for the mOH stretch of ligands were replaced by a broad
band, proving the coordination of phenol groups to the metal.
The electronic absorption spectra of complexes have been mea-
sured in dichloromethane in the 200–800 nm range. In all com-
plexes, the absorption maxima observed in the near-UV regions
545, UV–Vis in CH2Cl2: kmax, nm (e
, Mꢀ1 cmꢀ1): 284 (11752), 536
(3483).
2.2.2.5. Synthesis of FeLNEBu. Yield: 0.46 g (68%). Anal. Calc. for C39-
H61FeN2O4 (677.76 g/mol): C, 69.26; H, 9.01; N, 4.18%. Found: C,
69.01; H, 9.21; N, 4.13%. IR (KBr, cmꢀ1): 3446, 2954, 2906, 2865,
1590, 1524, 1469, 1374, 1301, 1256, 1203.50, 1166, 1088, 1022,
924, 877, 837, 807, 541, 476, UV–Vis in CH2Cl2: kmax, nm (e
, Mꢀ1
cmꢀ1): 280 (20767), 541 (5278).
(below 300 nm) are caused by
nolate units.
p
?
p
ꢁ transitions involving the phe-
The visible spectrum (between 400 and 700 nm) of FeLNEX com-
plexes showed that there are two absorption features in these
2.2.2.6. Synthesis of FeLNEOB. Yield: 0.52(83%). Anal. Calc. for C33H49-
FeN2O6 (625.60 g/mol): C, 63.41; H, 7.73; N, 4.55%. Found: C, 63.25;
H, 8.04; N, 4.47%. IR (KBr, cmꢀ1):3714, 3414, 2951, 2861, 1724,
1641, 1585, 1520, 1458, 1426, 1364, 1313, 1266, 1203, 1064,
spectra which are assigned to phenolate(
transfer (LMCT) transitions (Fig. 1, Table 1).
p
)-to-Fe(III)(d
p
ꢁ) charge
1022, 927, 869, 822, 792, UV–Vis in CH2Cl2: kmax, nm (e -
, Mꢀ1
cmꢀ1): 300 (15299), 558 (5086).
Table 1
kmax (nm)
e
((Mꢀ1 cmꢀ1) LMCT band of com-
plexes FeLNEX (X: C, B, M, BM, Bu and OB).
3. Results and discussion
FeLNEX
kmax (nm) (e
(Mꢀ1 cmꢀ1))
H2LNEX ]X: C, B, M, BM, Bu and OB [, were prepared from N,N0
dimethylethylenediamine, formaldehyde and 2,4-di-]Cl, Br, Me,
tBu and OMe[ phenol, in one step Mannich condensation. Amino-
phenol ligands are usually prepared in methanol solutions but
we describe herein the green synthesis when water is used as
the reaction medium. In fact, since aqueous formaldehyde is one
FeLNEC
500 (7714)
518 (5128)
529 (6197)
536 (3483)
541 (5278)
558 (5086)
FeLNEB
FeLNEM
FeLNEBM
FeLNEBU
FeLNEOB

T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
127
Table 2
Crystallographic and structure refinement data for compounds FeLNEC, FeLNEB and FeLNEM
FeLNEC
.
FeLNEB
FeLNEM
Identification code
e303abs
297abs
e300abs
Formula
Formula weight
C23H27Cl4FeN2O5
609.12
C23H27Br4FeN2 O5
786.96
C27H39FeN2O5
527.45
T (K)
293(2)
293(2)
293(2)
k (Å)
0.71073
0.71073
0.71073
Crystal system, space group
monoclinic, P21/n
monoclinic, P21/n
monoclinic, P21/n
Unit cell dimensions
a (Å)
b (Å)
c (Å)
8.4682(3)
15.1231(5)
21.2053(8)
90
8.7434(3)
15.1604(5)
21.3449(8)
90
8.4632(6)
15.2043(9)
21.6176(15)
90
a
(°)
b (°)
92.699(3)
90
2712.65(16)
4, 1.491
0.986
93.018(4)
90
2825.42(17)
4, 1.850
6.225
93.473(6)
90
2776.6(3)
4, 1.262
0.580
1124
c
(°)
V (Å3)
Z (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
1252
1540
Crystal size (mm)
h (°)
Limiting indices
0.4801 ꢂ 0.2766 ꢂ 0.1140
0.4628 ꢂ 0.2180 ꢂ 0.1339
0.3095 ꢂ 0.1342 ꢂ 0.0429
2.31–28.51
ꢀ9 6 h 6 11,
ꢀ20 6 k 6 19,
ꢀ28 6 l 6 27
2.35–28.37
2.34–28.36
ꢀ11 6 h 6 9,
ꢀ18 6 k 6 20,
ꢀ27 6 l 6 25
18256/6125 [R(int) = 0.0288]
26.00 99.9%
0.8959/0.6490
6125/0/316
ꢀ10 6 h 6 11,
ꢀ20 6 k 6 20,
ꢀ18 6 l 6 27
14108/5851 [R(int) = 0.0328]
24.80 94.0%
0.4895/0.1608
5851/0/316
Reflections collected/unique
Completeness to h
Max./min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
18668/6320 [R(int) = 0.1293]
26.00 99.9%
0.9755/0.8409
6320/0/316
0.843
1.065
0.948
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0514, wR2 = 0.1587
R1 = 0.0728, wR2 = 0.1686
1.593 and ꢀ0.424
R1 = 0.0380, wR2 = 0.1009
R1 = 0.0746, wR2 = 0.1079
1.388 and ꢀ0.594
R1 = 0.0653, wR2 = 0.1528
R1 = 0.2096, wR2 = 0.1912
0.787 and ꢀ0.441
Largest diff. peak and hole (e Aꢀ3
)
Table 3
Crystallographic and structure refinement data for compounds FeLNEBu, FeLNEBM and FeLNEOB
FeLNEBu
.
FeLNEBM
FeLNEOB
Identification code
Formula
Formula weight
T (K)
e302abs
39H61Fe N2 O4
e434a
C33 H49 Fe N2 O4
593.59
293(2)
0.71073
e402abs
C33 H49 Fe N2 O6
625.59
293(2)
0.71073
C
677.75
293(2)
0.71073
k (Å)
ꢀ
Crystal system, space group
Monoclinic, P21/c
Monoclinic, C2/c
Triclinic, P1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
11.3161(5)
13.6678(6)
14.8013(6)
78.202(4)
13.9901(5).
12.4394(5)
18.6196(7).
90
35.594(5)
13.8448(11)
14.0226(15)
90
a
(°)
b (°)
71.621(4)
68.081(4)
2005.62(15)
2, 1.122
0.413
734
96.777(4)
90
3217.7(2)
4, 1.225
0.506
1276
104.822(13)
90
6680.4(13)
8, 1.244
0.495
c
(°)
V (Å3)
Z (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
2680
Crystal size (mm)
h (°)
0.7899 ꢂ 0.4933 ꢂ 0.3242
0.66 ꢂ 0.42 ꢂ 0.05
0.42 ꢂ 0.35 ꢂ 0.12
2.12–28.47
2.20–28.27
2.08–28.60
Limiting indices
ꢀ15 6 h 6 14,
ꢀ17 6 k 6 16,
ꢀ16 6 l 6 19
13792/8822 [R(int) = 0.0368]
25.00 99.8%
0.8776/0.7360
8822/0/415
1.035
ꢀ18 6 h 6 18,
ꢀ13 6 k 6 15,
ꢀ22 6 6 l 6 23
21397/7055 [R(int) = 0.0500]
25.00 99.9%
0.9729 and 0.7313
7055/0/361
ꢀ44 6 h 6 47,
ꢀ17 6 k 6 17,
ꢀ18 6 l 6 17
22779/7706 [R(int) = 0.0813]
26.37 100.0%
0.9413/0.8186
7706/0/389
Reflections collected/unique
Completeness to h
Max./min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
0.951
0.895
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0568, wR2 = 0.1752
R1 = 0.0831, wR2 = 0.2068
0.637 and ꢀ0.527
R1 = 0.0435, wR2 = 0.1068
R1 = 0.0710, wR2 = 0.1145
0.354 and ꢀ0.343
R1 = 0.0608, wR2 = 0.1404
R1 = 0.1307, wR2 = 0.1659
0.505 and ꢀ0.625
Largest diff. peak and hole (e Aꢀ3
)
The position of LMCT bands is found to shift to higher wave-
lengths (lower energy) when electron donating substituents are on
the phenolate groups which would raise the energy of the frontier
orbitals of the ligand and thus minimize the ligand-to-iron gap [7].
3.1. Description of crystal structure
The diffraction experiment and the structure refinement for the
FeLNEC, FeLNEB, FeLNEM, FeLNEBM, FeLNEBu and FeLNEOB complexes

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T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
Table 4
Selected bond lengths (Å) and angles (deg) for compounds FeLNEC, FeLNEB and FeLNEM
.
FeLNEC
FeLNEB
FeLNEM
Bond lengths (Å)
Fe1–O1
Fe1–O2
Fe1–O3
Fe1–O4
1.913(2)
1.895(2)
1.991(2)
2.028(2)
2.274(3)
2.232(3)
Fe1–O1
Fe1–O2
Fe1–O3
Fe1–O4
Fe1–N1
Fe1–N2
1.901(3)
1.907(3)
1.992(4)
2.030(3)
2.235(4)
2.267(4)
Fe1–O1
Fe1–O2
Fe1–O3
Fe1–O4
Fe1–N1
Fe1–N2
1.885(4)
1.902(3)
2.061(4)
2.007(4)
2.215(4)
2.268(4)
Fe1–N1
Fe1–N2
Bond angles (°)
O2–Fe1–O1
O3–Fe1–O4
O1–Fe1–N1
O1–Fe1–N2
O3–Fe1–N1
O3–Fe1–N2
N2–Fe1–N1
96.54(10)
86.17(9)
85.11(9)
92.98(10)
91.51(10)
168.75(10)
79.58(10)
O1–Fe1–O2
O3–Fe1–O4
O1–Fe1–N1
O1–Fe1–N2
O3–Fe1–N1
O3–Fe1–N2
N1–Fe1–N2
96.06(14)
86.03(14)
85.88(14)
165.75(15)
168.56(14)
90.84(15)
79.88(15)
O1–Fe1–O2
O4–Fe1–O3
O1–Fe1–N1
O1–Fe1–N2
O3–Fe1–N1
O3–Fe1–N2
N1–Fe1–N2
96.99(15)
84.88(15)
87.43(16)
166.55(16)
86.54(16)
86.33(15)
79.26(16)
Table 5
Selected bond lengths (Å) and angles (deg) for compounds FeLNEBu, FeLNEBM and FeLNEOB
.
FeLNEBu
FeLNEBM
FeLNEOB
Bond lengths (Å)
Fe1–O1
Fe1–O2
Fe1–O3
Fe1–O4
1.9349(18)
1.878(2)
1.977(2)
2.063(2)
2.300(2)
2.203(2)
Fe1–O1
Fe1–O2
Fe1–O3
Fe1–O4
Fe1–N1
Fe1–N2
1.8802(14)
1.8716(14)
2.0022(14)
2.0753(15)
2.2420(17)
2.2400(17)
Fe1–O1
Fe1–O4
Fe1–O6
Fe1–O5
Fe1–N1
Fe1–N2
1.856(2)
1.906(2)
2.000(2)
2.048(2)
2.243(3)
2.270(3)
Fe1–N1
Fe1–N2
Bond angles (°)
O2–Fe1–O1
O3–Fe1–O4
O1–Fe1–N1
O1–Fe1–N2
O3–Fe1–N1
O3–Fe1–N2
N2–Fe1–N1
98.34(9)
83.94(10)
84.77(8)
99.05(8)
93.12(9)
168.05(9)
79.58(8)
O2–Fe1–O1
O3–Fe1–O4
O1–Fe1–N1
O1–Fe1–N2
O3–Fe1–N1
O3–Fe1–N2
N2–Fe1–N1
99.28(6)
84.58(6)
88.43(6)
95.14(6)
92.21(7)
167.01(6)
79.36(6)
O1–Fe1–O4
O6–Fe1–O5
O1–Fe1–N1
O1–Fe1–N2
O5–Fe1–N1
O5–Fe1–N2
N1–Fe1–N2
97.58(9)
85.05(9)
84.70(10)
163.03(10)
84.66(9)
85.12(9)
78.37(10)
Fig. 3. ORTEP diagram and atom labeling scheme for complex FeLNEB Ellipsoids are
plotted at 30% probability level.
Fig. 2. ORTEP diagram and atom labeling scheme for complex FeLNEC Ellipsoids are
plotted at 30% probability level.
reported here are summarized in Tables 2 and 3. The selected bond
lengths and angles are given in Tables 4 and 5.
In all structures reported here, the pairs of phenolic O atoms
and the N atoms of the ligand occupy the cis positions within the
Fe coordination sphere. Also the pair of acac oxygen atoms is
bound in the cis arrangement. Consequently, the Fe ion has a FeN2-
O4 coordination sphere which has an octahedral geometry (Tables
4 and 5).
The overall molecular architecture of FeLNEC, FeLNEB, FeLNEM
,
FeLNEBM and FeLNEOB complexes is similar. The tetradentate amine
bis(phenolate) ligands form a curved part of the Fe environment,
with the phenolic rings almost perpendicular to each other. The

T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
129
Fig. 7. ORTEP diagram and atom labeling scheme for complex FeLNEOB Ellipsoids are
plotted at 30% probability level.
Fig. 4. ORTEP diagram and atom labeling scheme for complex FeLNEM Ellipsoids are
plotted at 30% probability level.
acac ligands are bidentately coordinated to the central ion on the
convex side of the amine bis(phenolate) ligands. The observed con-
formation of ethylenediamine moiety of the ligands is synclinal,
with the N1–C8–C9–N2 torsion angle of ꢀ58.2(4)°, 56.5(6)°,
ꢀ58.6(6)° and ꢀ59.7(2)° for FeLNEC, FeLNEB, FeLNEM, FeLNEBM, respec-
tively. In FeLNEC, FeLNEB and FeLNEM all substituents of the phenolic
rings are co-planar with the rings, therefore not interfering with
the position of acac ligands. The methyl groups bound to the ligand
N atoms are positioned trans to each other, and are located on the
opposite sides of the central Fe1–N1–C8–C9–N2 chelate ring. In
such orientation, one of these N-Met moieties forms the weak
intramolecular interactions with the acac ligands (Figs. 2–7). Such
orientation has been found in Fe complexes of analogous ligands
[25–27]. Only in FeLNEBu complex, the N-Met groups are positioned
cis to each other. In FeLNEBM, FeLNEBu and FeLNEOB structures, the
bulky tBu groups and the N-Met form a hydrophobic pocket, in
which the acac ligand is accommodated. In all other complexes re-
ported in this paper, the substituents are positioned co-planar with
the phenolic rings and do not participate in the close interactions
with the acac ligand.
3.1.1. X-ray crystal structure of FeLNEC monohydrate
Fig. 5. ORTEP diagram and atom labeling scheme for complex FeLNEBM Ellipsoids are
plotted at 30% probability level.
The asymmetric part of the reported structure consists of the Fe
complex molecule containing LNEC ligand forming four bonds to the
central Fe(III) ion, the acac ligand and the water molecule, the last
one has not bound to the central Fe ion (Fig. 2). The phenolate O1
and O2 of H2LNEC form the shortest bonds to the Fe(III), the dis-
tances being 1.913(2) and 1.895(2) Å, respectively, while the nitro-
gen atoms N1 and N2 form the longest bonds within the
coordination sphere, the distances being 2.274(3) and 2.232(3) Å,
respectively. The acac O3 and O4 participate in the Fe–O bonds
of 1.991(2) and 2.028(2) Å, respectively. The largest deformation
from the expected 90/180° values is found for O1–Fe1–N2 angle
of 165.75(15)°.
Three chelate rings are formed by the LNEC atoms and Fe ion. The
Fe1–N1–C8–C9–N2 ring has a conformation twisted on C8–C9,
while Fe1–O1–C1–C6–C7–N1 and Fe1–O2–C16–C11–C10–N2 rings
have an envelope conformation. Also the chelate ring formed by
the acac ligand has an envelope conformation.
The valence geometry of the LNEC ligand is typical. The C–Cl dis-
tances vary from Cl1–C2 1.737(3) to Cl3–C13 1.748(3) Å. The O1–
C1 and O2–C16 distances are 1.300(4) and 1.315(4) Å, respectively,
and are similar to those found in other FeLNEX complexes reported
Fig. 6. ORTEP diagram and atom labeling scheme for complex FeLNEBu Ellipsoids are
plotted at 30% probability level.

130
T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
here. The N1–C8–C9–N2 torsion angle of ꢀ58.2(4)° reflects the
strain caused by the tetradentate coordination of the ligand. The
spatial orientation of two phenolic moieties is similar to that found
for other complexes, with the dihedral angle between their planes
being 74.6°. Position of the acac, as described with the dihedral an-
gles between that plane and C1–C6 and C11–-C16 rings being
77.81° and 86.12°, respectively, is also similar to that found for
deformation from the expected 90/180° values is found for O1–
Fe1–N2 angle of 166.55(16)°.
Three chelate rings are formed by the LNEM atoms and Fe ion.
The Fe1–N1–C8–C9–N2 ring has a conformation twisted on C8–
C9, while Fe1–O1–C1–C6–C7–N1 and Fe1–O2–C16–C11–C10–N2
rings have an envelope and twist boat conformation, respectively.
Also the chelate ring formed by the acac ligand has an envelope
conformation.
the brominated analog in FeLNEB
.
There is a H-bond formed between the water molecule O5–
The valence geometry of the LNEM ligand is typical. The O1–C1
and O2–C16 distances are 1.331(6) and 1.319(6) Å, respectively.
The N1–C8–C9–N2 torsion angle is ꢀ58.6(6)°, reflecting the strain
caused by the tetradentate coordination of the LNEM ligand. Two
phenolic moieties are almost perpendicular to each other, with
the dihedral angle between the ring planes being 74.0°. Also the
plane of the acac ligand is almost perpendicular to the phenolic
rings, the dihedral angles between that plane and C1–C6 and
C11–C16 rings are 89.43° and 75.93°, respectively.
H51A and the Cl2 atom, the O5ꢃ ꢃ ꢃCl2[xꢀ1,y,z] distance being
3.773 Å. Analysis of the crystal packing reveals the C–Hꢃ ꢃ ꢃ
p inter-
actions involving the N-Met group, with the distances to the cen-
ters of gravity C17–H17Cꢃ ꢃ ꢃCg(C11–C16) [3/2ꢀx,ꢀ1/2+y,1/2ꢀz] of
2.89 Å and the intramolecular C17–H17Aꢃ ꢃ ꢃCg(O3–C20–C21–
C22–O4–Fe1) of 2.62 Å, almost identical to those reported for
FeLNEB
.
There is a series of H-bonds involving the water O31 molecules,
3.1.2. Crystal structure of FeLNEB monohydrate
with the O31ꢃ ꢃ ꢃO31 [ꢀx+1,ꢀy,ꢀz+1] distance of 2.410 Å. Analysis
The asymmetric part of the reported structure consists of the Fe
complex molecule containing LNEB ligand forming four bonds to the
central Fe(III) ion, the acac ligand and the water molecule, the last
one has not bound to the central Fe ion (Fig. 3). The Fe ion has a
FeN2O4 coordination sphere which has an octahedral geometry
(Table 4). The phenolate O1 and O2 of LNEB form the shortest bonds
to the Fe(III), the distances being 1.901(3) and 1.907(3) Å, respec-
tively, while the nitrogen atoms N1 and N2 form the longest bonds
within the coordination sphere, the distances being 2.235(4) and
2.267(4) Å. The acac O3 and O4 coordinate to Fe1, with the Fe–O
distances being 1.992(4) and 2.030(3) Å, respectively. The largest
deformation from the expected 90/180° values is found for O1–
Fe1–N2 angle of 165.75(15)°.
of the crystal packing reveals the intramolecular C–Hꢃ ꢃ ꢃ
p interac-
tions involving the N-Met group, with the distances to the centers
of gravity C20–H20Cꢃ ꢃ ꢃCg(C1–C6) [1/2ꢀx,ꢀ1/2+y,1/2ꢀz] of 2.80 Å.
3.1.4. X-ray crystal structure of FeLNEBM
The asymmetric part of the reported structure consists of the Fe
complex molecule containing LNEBM ligand forming four bonds to
the central Fe(III) ion and the acac ligand (Fig. 5). Within the coor-
dination sphere, the pairs of phenolic O atoms and N atoms of the
LNEBM ligand, as well as acac oxygen atoms occupy the cis positions.
The Fe ion has a FeN2O4 coordination sphere of an octahedral
geometry (Table 5). Similar to other structures reported here, the
phenolate O1 and O2 of LNEBM form the shortest bonds to the
Fe(III), the distances being 1.8802(14) and 1.8716(14) Å, respec-
tively. The bonds formed by N1 and N2 nitrogen atoms are the lon-
gest, the distances being 2.2420(17) and 2.2400(17) Å,
respectively. The acac O3 and O4 coordinate to Fe1, with the Fe–
O distances being 2.0022(14) and 2.0753(15) Å, respectively. The
largest deformation from the expected 90/180° values is found
for O2–Fe1–N1 angle of 166.30(6)°.
The chelate rings formed by the Fe ion and LNEB and acac atoms
have a conformation analogous to that described for FeLNEC
complex.
The valence geometry of the LNEB ligand is typical. The C–Br dis-
tances vary from 1.889(5) to 1.905(5) Å. The O1–C1 and O2–C16
distances are 1.319(5) and 1.303(5) Å, respectively. The N1–C8–
C9–N2 torsion angle is 56.5(6)°, reflecting the strain caused by
the tetradentate coordination of the LNEB ligand. The presence of
the ethylenediamine bridge between two phenolic moieties results
on the almost perpendicular orientation of the phenolic rings, with
the dihedral angle between their planes being 73.2°. Also the plane
of the acac ligand is almost perpendicular to the phenolic rings, the
dihedral angles between that plane and C1–C6 and C11–C16 rings
are 89.43° and 75.93°, respectively.
Three chelate rings are formed by the LNEBM atoms and Fe ion.
The Fe1–N1–C8–C9–N2 ring has a conformation of an envelope
on C9, the Fe1–O1–C1–C6–C7–N1 ring has a half-chair conforma-
tion, and Fe1–O2–C16–C11–C10–N2 ring has a screw-boat confor-
mation. The chelate ring formed by the acac ligand has an envelope
conformation.
There is a H-bond formed between the water molecule O5–
The valence geometry of the LNEBM ligand is typical. The O1–C1
and O2–C16 distances are 1.329(2) and 1.330(2) Å, respectively.
The N1–C8–C9–N2 torsion angle is ꢀ59.7(2)°. The presence of
the CNC2NC bridge between two phenolic moieties results on the
almost perpendicular orientation of the phenolic rings, with the
dihedral angle between their planes being 84.5°. Also the plane
of the acac ligand is almost perpendicular to the phenolic rings,
the dihedral angles between that plane and C1–C6 and C11–C16
rings are 86.27° and 85.29°, respectively.
H51B and the Br atom, the O5ꢃ ꢃ ꢃBr3[x ꢀ 1,y,z] distance being
3.813 Å. Analysis of the crystal packing reveals the C–Hꢃ ꢃ ꢃ
p inter-
actions involving the N-Met group, with the distances to the cen-
ters of gravity C18–H18Aꢃ ꢃ ꢃCg(C1–C6) [1/2ꢀx,1/2+y,1/2ꢀz] of
2.85 Å and the intramolecular C18–H18Cꢃ ꢃ ꢃCg(O3–C20–C21–C22–
O4–Fe1) of 2.68 Å.
3.1.3. X-ray crystal structure of FeLNEM
Analysis of the crystal packing reveals the C–Hꢃ ꢃ ꢃ
p interactions
The asymmetric part of the FeLNEM structure consists of the Fe
complex molecule containing LNEM ligand, the acac ligand and
the water molecule, the last one has not bound to the central Fe
ion (Fig. 4).
involving the C1–C6 phenyl ring and tBu group C19–
H19Cꢃ ꢃ ꢃCg(C1–C6)[ꢀx,1ꢀy,ꢀz] and C24 methyl group C24–
H24Cꢃ ꢃ ꢃCg(C1–C6)[1ꢀx,1ꢀy,ꢀz]. The respective distances between
hydrogen atoms and the ring gravity center are 2.91 and 2.96 Å,
respectively.
Geometry of the FeN2O4 coordination sphere is octahedral (Ta-
ble 4). The phenolate O1 and O2 of LNEM form the shortest bonds to
the Fe(III), the distances being 1.885(4) and 1.902(3) Å, respec-
tively, while the nitrogen atoms N1 and N2 form the longest bonds
within the coordination sphere, the distances being 2.215(4) and
2.268(4) Å. The acac O3 and O4 coordinate to Fe1, with the Fe–O
distances being 2.061(4) and 2.007(4) Å, respectively. The largest
3.1.5. X-ray crystal structure of FeLNEBu
The asymmetric part of the structure consists of the FeLNEBu
complex molecule. The LNEBu ligand forms four bonds to the central
Fe(III) ion (Fig. 6).

T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
131
Architecture of the complex molecule is different from those
found in FeLNEC, FeLNEB and FeLNEM reported in this paper. In
FeLNEBu complex, the conformation of the N1–C8–C9–N2 bridge is
ꢀ61.0(3)°, and both N-Met groups are positioned on the same side
of the Fe–N1–C8–C9–N1 chelate ring, being cis to each other. In all
other complexes reported here, these methyl groups are positioned
on different sides of the corresponding ring. Such differences in the
orientation of the analogous methyl groups have been reported be-
fore for similar complexes [25]. On the other hand, in complexes
containing LNEBu and monodentate axial Cl, Br or nitrate ligands,
[26,27] the N-Met groups are positioned trans to each other as
for FeLNEC, FeLNEB and FeLNEM reported here.
The octahedral geometry of the Fe coordination sphere is simi-
lar to those found in other complexes reported here (Table 5). The
phenolate O1 and O2 of LNEBu form the shortest bonds to the Fe(III),
the distances being 1.9349(18) and 1.878(2) Å, respectively, while
the nitrogen atoms N1 and N2 form the longest bonds within the
coordination sphere, the distances being 2.300(2) and 2.203(2) Å,
respectively. The acac O3 and O4 participates in the Fe–O bonds
of 1.977(2) and 2.063(2) Å, respectively. The largest deformation
from the expected 90/180° values is found for O2–Fe1–N1 angle
of 166.14(9)°.
The chelate rings formed by the Fe ion and LNEBu and acac atoms
have a conformation analogous to that described for FeLNEB and
FeLNEC complexes. Only Fe1–O1–C1–C6–C7–N1 ring has a twist-
boat conformation.
Fig. 8. Temperature dependent susceptibility
v(T) and inverse susceptibility
vꢀ1(T)(inset) of FeLNEX (X: C, B, M, BM, Bu and OB) measured in magnetic field of
H = 1000 Oe.
The valence geometry of the LNEBu ligand is typical. The O1–C1
and O2–C16 distances are 1.350(3) and 1.335(3) Å, respectively,
and are significantly longer than those found in complexes of chlo-
rinated LNEC or brominated LNEB ligands. The N1–C8–C9–N2 torsion
angle of ꢀ61.0(3)° and is similar to the values found for FeLNEB and
FeLNEC complexes, although statistically significant differences val-
ues are observed.
The spatial orientation of two phenolic moieties is different
from those found for other complexes, with the dihedral angle be-
tween their planes of 52.1°, being approximately 20° smaller than
the values calculated for FeLNEB, FeLNEC and FeLNEM complexes. The
acac ligand is positioned in the narrow crevice between the N-Met
and tBu moieties. The dihedral angles between the acac plane and
C1–C6 and C11–C16 rings are 81.37° and 71.89°, respectively, is
also similar to that found for complexes of the brominated and
chlorinated ligands.
C10–N2 rings have an envelope conformation. The chelate ring
formed by the acac ligand has a screw-boat conformation.
The valence geometry of the LNEOB ligand is typical. The O1–C1
and O2–C16 distances are 1.328(4) and 1.342(3) Å, respectively.
The methoxy groups form the C4–O2 and C13–O3 bonds of
1.369(5) and 1.396(4) Å, respectively. The rotational disorder was
detected for the O2–C21 methoxy group, with the occupancy of
both alternative Met position estimated as 50% during the refine-
ment. Both methoxy groups are co-planar with the phenolic rings,
the torsion angles being C3–C4–O2–C21 178.5(10), C3–C4–O2–
C21B ꢀ7.9(12) and C12–C13–O3–C24 5.2(5)°. The N1–C8–C9–N2
torsion angle is ꢀ58.7(4)°, and is similar to that found in all other
structures reported here. The dihedral angle of 69.95° between two
phenolic moieties is smallest for the series of the complexes re-
ported here. Only in the FeLNEBu complex with the flat architecture,
that angle is significantly smaller, being 52.1°. Also the plane of the
acac ligand is almost perpendicular to the phenolic rings, the dihe-
dral angles between that plane and C1–C6 and C11–C16 rings are
81.57° and 89.30°, respectively.
Analysis of the crystal packing reveals some hydrophobic inter-
molecular interactions. There is the C–Hꢃ ꢃ ꢃ
p interaction involving
the tBu C28–H28C group and the C11–C16[2ꢀx,ꢀy,1ꢀz] ring, with
The analysis of FeLNEOB structure revealed an intramolecular
interaction between C23 methyl and the gravity center of the che-
late ring formed by acac ligand, the C23–H23Aꢃ ꢃ ꢃCg(Fe1–O5–O65)
of 2.52 Å. Analysis of the crystal packing reveals the C23–
H23Cꢃ ꢃ ꢃO3[1/2ꢀx,1/2+y,1/2ꢀz] interaction with the Cꢃ ꢃ ꢃO distance
of 3.346 Å.
the Hꢃ ꢃ ꢃCg distance of 2.73 Å.
3.1.6. X-ray crystal structure of FeLNEOB
The asymmetric part of the reported structure consists of the Fe
complex molecule containing LNEOB ligand forming four bonds to
the central Fe(III) ion and the acac ligand (Fig. 7). Within the coor-
dination sphere, the pairs of phenolic O atoms and N atoms of the
LNEOB ligand, as well as acac oxygen atoms occupy the cis positions.
The Fe ion has a FeN2O4 coordination sphere of an octahedral
geometry (Table 5). Similar to other structures reported here, the
phenolate O1 and O4 of LNEOB form the shortest bonds to the Fe(III),
the distances being 1.856(2) and 1.906(2) Å, respectively. Within
the coordination sphere the bonds formed by N1 and N2 nitrogen
atoms are the longest, the distances being 2.243(3) and 2.270(3) Å,
respectively. The acac O5 and O6 coordinate to Fe1, with the Fe–O
distances being 2.048(2) and 2.000(2) Å, respectively. The largest
deformation from the expected 90/180° values is found for O1–
Fe1–N2 angle of 163.03(10)°.
In the FeLNEOB complex, the acac ligand is positioned between
the C23 methyl bound to N1 and C20 methyl of the tBu group
Table 6
Calculated parameters C and h from the fit of the measured data with Eq. (2). The
effective magnetic moment leff per iron ion was calculated using
a relation
pffiffiffiffiffiffi
leff
¼
8C [28].
C (emu K/mol)
h (K)
leff (BM)
FeLNEB
4.1
4.0
3.7
3.6
3.3
4.0
ꢀ1.8
ꢀ1.5
3.3
ꢀ0.6
ꢀ0.9
ꢀ0.1
5.7
5.7
5.4
5.4
5.1
5.7
FeLNEM
FeLNEC
FeLNEBu
FeLNEBM
FeLNEOB
The chelate rings formed by the LNEOB atoms and Fe ion have a
following conformation: the Fe1–N1–C8–C9–N2 ring is twisted on
C8–C9, while the Fe1–O1–C1–C6–C7–N1 and Fe1–O4–C16–C11–

132
T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
Table 7
Electrode peak potentials for oxidation and reduction of complexes FeLNEX (X: C, B, M, BM, Bu and OB).
E1ox/V
E2ox/V
E3ox/V
E4ox/V
E4red/V
E3red/V
E2red/V
E1red/V
*
FeLNEC
ꢀ1.06
ꢀ1.09
-
ꢀ1.67
ꢀ1.3
ꢀ1.59
-
-
-
-
0.95
0.87
0.68
0.20
0.66
0.14
1.23
1.17
1.04
0.63
1.03
0.45
-
-
-
-
-
-
ꢀ1.15
ꢀ1.23
-
ꢀ1.77
ꢀ1.45
ꢀ1.67
FeLNEB
0.65
0.60
0.12
0.58
0.06
FeLNEM
FeLNEBM
FeLNEBu
FeLNEOB
ꢀ0.50
0.56
0.95
0.37
-
ꢀ0.79
ꢀ0.85
-
-
*
Redox behavior ill-defined.
bound to C2. Such arrangement is a consequence of the presence of
bulky tBu group and N-Met near the Fe center, and is found also in
FeLNEBu and FeLNEBM
.
3.2. Magnetic susceptibility measurement
Magnetic susceptibility of powdered samples of FeLNEC, FeLNEB
,
FeLNEM, FeLNEBM, FeLNEBu and FeLNEOB were measured in a magnetic
field of 1000 Oe as a function of temperature in the range 2–300 K
with a Quantum Design MPMS-XL-5 magnetometer. The measured
data were corrected for the sample holder contribution, for the
temperature-independent Larmor diamagnetic susceptibility ob-
tained from the Pascal’s tables, and temperature independent para-
magnetism [28].
Temperature variation of susceptibility
v(T) is shown in Fig. 8.
The susceptibilities of all complexes increase with decreasing tem-
perature and are practically the same for all investigated com-
plexes. Only the inverse susceptibility graph vꢀ1(T) shows small
differences between the complexes.
As all inverse susceptibilities show linear temperature depen-
dence, we applied a Curie–Weiss law in order to describe the mea-
sured data:
Fig. 9. Cyclic voltammogram of FeLNEBu in CH2Cl2 at ꢀ70 °C (sc 20 mVsꢀ1) .
ð¼ C=ðT ꢀ 00ð00Þ
ð2Þ
The obtained parameters C and h from the fit procedure with Eq.
(2) and calculated effective magnetic moment
collected in Table 6.
leff per iron ion are
The effective moments are between 5.4 and 5.7 Bohr magnetons
(the magnetic moments recorded at 2–300 K). The values are close
enough to the expected value for high spin Fe(III) of 5.9 BM [29]
and thus confirming a high spin iron(III) in the structure.
The Curie–Weiss temperatures h in Table 6 that are of the order
of few Kelvins should be considered as additional fit parameters
only, which slightly improve the fits rather than the indication of
an antiferromagnetic or ferromagnetic coupling between the para-
magnetic ion.
3.3. Electrochemistry
Cyclic voltammogram (CV) of complexes have been recorded in
CH2Cl2 solutions containing 0.1 M [(nBu)4N]ClO4 as a supporting
electrolyte.
ox
This research reveals that there are two oxidation peaks (E3
and E4ox) for all complexes with a similar small difference in their
redox potentials. Selected results are collected in Table 7. Typical
cyclic voltammograms (CV) of FeLNEBu, FeLNEBM and FeLNEOB, are
presented in Figs. 9–12. The similarity of E3 and E4 values for
all complexes in the range of 0.1–1.5 V suggests the same oxidation
mechanism for all complexes.
ox
ox
Fig. 10. Cyclic voltammograms of FeLNEBu, FeLNEOB and FeLNEBM in CH2Cl2 at ꢀ70 °C
(sc 20 mVsꢀ1).
These redox processes might be attributed to the ligand cen-
tered redox processes in which phenolate group yields phenoxyl
radical in the complex, but there is no direct evidence available yet.
Comparison of the oxidation potentials of complexes suggesting
that anodic oxidation processes are sensitive to the involved
change in electron accepting of substituents on phenolate moieties
of the ligands (Table 7).
On the other hand, the oxidation potentials of FeLNEX (X: C, B, M,
BM, Bu and OB), with electron accepting ligands are more positive
than those for complexes with electron donating groups due to the

T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
133
been structurally characterized by single crystal X-ray diffraction.
X-ray structure analysis has revealed that all complexes are six
coordinate and Fe(III) centers were surrounded by two phenolate
oxygen atoms, two amine nitrogens and two oxygen atoms of ace-
tylacetonate ligand similar to the proposed catechol-bound inter-
mediate for catechol dioxygenase. In FeLNEBu two of N-methyl
groups occupy the cis position relative to each other, while in all
other complexes reported here, the orientation is trans. Magnetic
moment measurements confirm paramagnetic iron(III) in mono-
mer complexes. All complexes undergo a metal-centered reduction
and a ligand-centered oxidation. The oxidation potentials of com-
plexes suggest that anodic oxidation processes are sensitive to
the electron accepting properties of substituents on phenolate
moieties of the aminophenol ligands.
Acknowledgments
Authors are grateful to the Institute for Advanced Studies in Ba-
sic Sciences (IASBS), Nicolaus Copernicus University and University
of Ljubljana. E. Safaei gratefully acknowledges the support by the
Institute for Advanced Studies in Basic Sciences (IASBS) Research
Council under Grant No. G2012IASBS127.
Fig. 11. Cyclic voltammograms of FeLNEBu, FeLNEOB and FeLNEBM in CH2Cl2 at ꢀ70 °C
(sc 20 mVsꢀ1).
Appendix A
The crystallographic data have been deposited with the Cam-
bridge Crystallographic Data Centre, the CCDC numbers, 875144,
875145, 875146, 875147, 875148 and 875149 for FeLNEC, FeLNEB
,
FeLNEM, FeLNEBu, FeLNEBM and FeLNEOB respectively.
,
These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
References
[1] T.D.H. Bugg, G. Lin, Chem. Commun. (2001) 941.
[2] L. Que, R.Y.N. Ho, Chem. Rev. 96 (1996) 2607.
[3] T. Funabiki, Oxygenases and model systems, in: R. Ugo, B.R. James (Eds.),
Catalysis by Metal Complexes, vol. 19, Kluwer, Dordrecht, 1997. and Refs.
therein.
[4] R.L. Crawford, D.L. Crawford, Enzyme Microb. Technol. 6 (1984) 434.
[5] F. Li, M. Wang, P. Li, T. Zhang, L. Sun, Inorg. Chem. 46 (2007) 9364.
[6] S. Harayama, M. Kok, E.L. Neidle, Annu. Rev. Microbial. 46 (1992) 565.
[7] R. Yamahara, S. Ogo, Y. Watanabe, T. Funabiki, K. Jitsukawa, H. Masuda, H.
Einaga, Inorg. Chim. Acta 300–302 (2000) 587.
[8] Y. Hitomi, M. Yoshida, M. Higuchi, H. Minami, T. Tanaka, T. Funabiki, J. Inorg.
Biochem. 99 (2005) 755.
[9] M. Merkel, M. Pascaly, B. Krebs, J. Astner, S.P. Foxon, S. Schindler, Inorg. Chem.
44 (2005) 7582.
[10] P. Mialane, L. Tchertanov, F. Banse, J. Sainton, J.-J. Girerd, Inorg. Chem. 39
(2000) 2440.
Fig. 12. Cyclic voltammograms of FeLNEBu in CH2Cl2 at ꢀ70 °C (sc 20–1000 mVsꢀ1).
[11] M. Pascaly, M. Duda, F. Schweppe, K. Zurlinden, F.K. Muller, B. Krebs, J. Chem.
Soc. Dalton Trans. 6 (2001) 828.
[12] M. Velusamy, R. Mayilmurugan, M. Palaniandavar, J. Inorg. Biochem. 99 (2005)
1032.
[13] R.B. Lauffer, R.H. Heistand, L. Que, Inorg. Chem. 22 (1983) 50.
[14] M. Merkel, F.K. Müller, B. Krebs, Inorg. Chim. Acta 337 (2002) 308.
[15] S. Ogo, R. Yamahara, T. Funabiki, H. Masuda, Y. Watanabe, Chem. Lett. 10
(2001) 1062.
harder oxidation of phenolate ligands to the corresponding phe-
noxyl radical cations.
These ligand-centered voltammograms are electrochemically
quasi-reversible, based on deviation of
aration of the oxidation and reduction peaks; the value of
reversible peaks is 1).
D
Ep from 1 (
D
Ep is the sep-
Ep for
D
[16] M.S. Shongwe, C.H. Kaschula, M.S. Adsetts, E.W. Ainscough, A.M. Brodie, M.J.
Morris, Inorg. Chem. 44 (2005) 3070.
[17] M. Velusamy, R. Mayilmurugan, M. Palaniandavar, Inorg. Chem. 43 (2004)
6284.
[18] M. Velusamy, M. Palaniandavar, R.S. Gopalan, G.U. Kulkarni, Inorg. Chem. 42
(2003) 8283.
The metal-centered voltammograms have been observed in the
negative potential range, what corresponds to the FeIII/FeII reduc-
tion of iron complexes.
[19] R. Viswanathan, M. Palaniandavar, T. Balasubramanian, T.P. Muthiah, Inorg.
Chem. 37 (1998) 2943.
4. Conclusions
[20] Y. Zang, J. Kim, Y. Dong, E.C. Wilkinson, E.H. Appelman, L. Que, J. Am. Chem.
Soc. 119 (1997) 4197.
}
[21] G.M. Sheldrick, SHELXS97 and SHELXL97, University of Gottingen, Germany, 1997.
A series of iron complexes have been synthesized and charac-
terized by IR, UV–Vis, elemental analysis and cyclic voltammetry
techniques. Complexes FeLNEX (X: C, B, M, BM, Bu and OB), have
[22] CrysAlis CCD171 and RED171 package of programs, Oxford Diffraction, 2000.
ˇ ´
[23] E. Safaei, I. Saberikia, A. Wojtczak, Z. Jaglicic, A. Kozakiewicz, Polyhedron 30
(2011) 1143.

134
T. Karimpour et al. / Inorganica Chimica Acta 395 (2013) 124–134
ˇ ´
[24] E. Safaei, H. Sheykhi, A. Wojtczak, Z. Jaglicic, A. Kozakiewicz, Polyhedron 30
(2011) 1219.
[27] K. Hasan, C. Fowler, P. Kwong, A.K. Crane, J.L. Collins, Ch.M. Kozak, Dalton
Trans. (2008) 2991.
[25] P. Mialane, E. Anxolabéhère-Mallart, G. Blondin, A. Nivorojkine, J. Guilhem, L.
Tchertanova, M. Cesario, N. Ravi, E. Bominaar, J.-J. Girerd, E. Münck, Inorg.
Chim. Acta 263 (1997) 367.
[28] O. Kahn, Molecular Magnetism, VCH Publishing, 1993.
[29] N.W. Ashcroft, N.D. Mermin, Solid State Physics, Saunders College Publishing,
USA, 1976.
[26] J.B.H. Strautmann, S.D. George, E. Bothe, E. Bill, T. Weyhermùller, A. Stammler,
H. Bögge, T. Glaser, Inorg. Chem. 47 (2008) 6804.